What is the key advantage of Write-Behind over synchronous Write-through?

The primary advantage of Write-behind is performance and latency reduction. Unlike synchronous Write-through, which waits for the database to confirm a write, Write-behind updates the cache immediately and queues the database operation to run in the background. This prevents database bottlenecks from impacting application responsiveness.

How does NCache handle failed background writes in Write-behind mode?

NCache maintains a fault-tolerant 'Failed Operations Queue'. If a background write to the data source fails, the operation is re-queued and retried based on your configured retry settings and eviction ratios, ensuring eventual consistency with the backend.

What is database throttling in the context of NCache Write-behind?

Throttling is managed via the 'Operations per second' setting. It allows administrators to limit the rate of background writes to the database, protecting the backend data source from being overwhelmed during high-traffic bursts in the distributed cache cluster.

Configure Write-through for Write-behind Cache Operations

The Write-behind feature in NCache allows cache updates (Add, Update, Remove) to be immediately acknowledged by the application while the corresponding data source operations are queued for execution in the background. This enables asynchronous data persistence, reducing application latency and preventing database bottlenecks during high-throughput scenarios. The Write-behind process can be configured to control performance through options like batching, rate limiting (operations per second), retry queues, and eviction ratio, all of which can be adjusted in the NCache Management Center or via PowerShell cmdlets.

Important

For .NET, before deploying your .dll files, ensure you have the appropriate .NET Version installed as discussed in the NCache Installation Guide.

Using the NCache Management Center

Launch the NCache Management Center by browsing to http://localhost:8251 or <server-ip>:8251.
In the left navigation bar, click on Clustered Caches or Local Caches, based on the cache to which the backing source will be configured. Against the cache name, click on View Details.
Make sure that the cache is stopped.

NCache Management Center showing the 'View Details' button for a cache, with the cache stopped, ready to configure the Write-through and Write-behind settings.

This opens up the detailed configuration page for the cache. Go to the Advanced Settings tab and click on Backing Source in the left bar.
Configure a Write-through provider as explained in Configuring Write-through Provider.

NCache Management Center displaying the 'Write-through' provider configuration screen with the 'Enable Batching' checkbox selected and Write-behind settings such as batch interval and operation delay configured.

Once here, you can change or specify the values as per your application requirement(s).
- Select the Enable Batching checkbox to perform all Write-behind operations on the data source in bulk/batches. You can also configure the Batch-interval(s) and Operation-delay(ms) for the batching mode.
- Change the value for Operations per second, to control how many Write-behind operations will be performed on the data source in a second.
- You can also configure the Failed operations queue limit. This queue is used to re-queue the failed operations and will be retried on the data source.
- The Failed operations eviction ratio specifies the eviction ratio percentage to evict the most retried operations when the queue is full.
Once you have added the Write-through provider, deploy the provider through the Deploy Backing Source Providers which requires the assemblies to be deployed over NCache.

NCache Management Center showing the 'Deploy Backing Source Providers' screen, where the Write-through provider assemblies are deployed for use with Write-behind caching.

After applying all the changes, click on Save Changes.

Using Command Line Tools

You can also use Command Line Tools to configure Write-through, as discussed below.

Configure Write-behind

The Add-BackingSource cmdlet enables users to configure backing source (Write-through) provider for the specified cache. The following command configures Writer1 as a Write-through provider on demoCache with Write-behind enabled.

Windows
Linux

Add-BackingSource -CacheName demoCache -AssemblyPath C:\Providers.dll -Class WriteThru.Writer -ProviderName Writer1 -WriteThru -IsBatching

add-backingsource -cachename demoCache -assemblypath /usr/Provider.dll -class WriteThru.Writer -providername Writer1 -writethru -isbatching

Remove Write-behind

The Remove-BackingSource cmdlet removes the pre-configured backing source providers (Write-through) from the cache or a specified server. The following command removes the pre-configured Write-behind provider named Writer1 from demoCache.

Windows
Linux

Remove-BackingSource -CacheName demoCache -ProviderName Writer1 –WriteThru

remove-backingsource -cachename demoCache -providername Writer1 -writethru